1. Field of the Invention
The present invention relates to a thermal transfer printer using a ribbon cassette, and more particularly to a thermal transfer printer capable of performing the hot peeling and the cool peeling of the ink ribbon by selectively operating the peeling roller.
2. Description of the Prior Art
FIG. 12 shows a conventional thermal transfer printer, which includes a frame 1. A flat platen 2 is provided at the center of this frame 1, so that its printing surface is disposed vertically. A carriage shaft 3 is disposed in front of and below the platen 2, so as to be disposed in parallel with each other.
A guide 4, formed in a flange-like shape, is provided at the front edge of the frame 1. A carriage 5 is mounted on the carriage shaft 3 and the guide 4 so that the carriage 5 can cause reciprocatory motions along these carriage shaft 3 and guide 4. Provided on the edge of the carriage 5 is a thermal head 6, which is disposed to confront with the platen 2 and driven by a driving mechanism (not shown) so as to be brought into contact with the platen 2 or shifted away from the platen 2.
The carriage 5 has an upper surface, on which a ribbon cassette (not shown) is detachably installed. The ribbon cassette accommodates an ink ribbon, and guides this ink ribbon to enter between the thermal head 6 and the platen 2. Also provided on the upper surface of the carriage 5 are a take-in bobbin 7 for taking in the ink ribbon of the ribbon cassette and a feed bobbin 8 for feeding the ink ribbon.
Behind the platen 2, there is provided a paper insertion opening 9 for feeding a sheet of paper forward beyond the platen 2. A paper feed roller 10 is disposed adjacent to the paper insertion opening 9 to feed the paper at a predetermined speed. This paper feed roller 10 is paired with a press roller 11, which is disposed rotatably just beneath and pressed against the paper feed roller 10. A paper feed motor 13 is provided on one side surface of the frame 1. This paper feed motor 13 drives the paper feed roller 10 through a transmission gear train 12 to cause rotation. Thus, the paper inserted into the paper insertion opening 9 is sandwiched by these paper feed roller 10 and the press roller 11 and conveyed by the driving force of the paper feed motor 13.
In the above-described conventional printer, the paper is inserted from the paper insertion opening 9 and sandwiched between the paper feed roller 10 and the press roller 11. And, the paper is conveyed at a predetermined speed in a direction normal to the shifting direction of the carriage 5 by rotating the paper feed roller 10 by the paper feed motor 13.
On the other hand, the carriage 5 is shifted under the condition the thermal head 6 is pressed against the paper at a predetermined pressure. Meanwhile, the take-in bobbin 7 is rotated to take in the ink ribbon of the ribbon cassette. The thermal head 6 is driven on the basis of desired printing signals. Thus, the printing operation can be carried out preferably.
By the way, various kinds of papers are used as printing papers. For example, generally known is a normal paper. An OHP sheet, made of plastic sheet having light permeability and used for the overhead projector (OHP), is also known as a printing paper. This OHP sheet, however, requires another ink ribbon different from for the normal paper.
The ink ribbon 14 used for the normal papers is, for example, constituted as shown in FIG. 13(A). A base member 15 is made of resin film such as polyethylene terephthalate. An ink layer 16, made by mixing resin and color such as carbon, is formed on the surface of this base member 15. Furthermore, an overcoat layer 17, made of high-viscous material such as polyamide, is formed on the surface of this ink layer 16.
Another example of the ink ribbon 14 is shown in FIG. 13(b). This ink ribbon 14 further includes a peeling layer 18 made of wax and having thermal solubility, which is interposed between the base member 15 and the ink layer 16.
In the case where this kind of ink ribbon 14 is used for printing normal papers, the thermal head 6 is driven to perform the hot peeling operation. That is, the ink ribbon 14 is peeled off from the normal paper during the time when the melted ink layer 16 is still maintained at hot temperature in the partly melted condition. For this reason, it is necessary to shorten the distance between the printing portion of the thermal head 6 and the peeling portion of the ink ribbon 14.
On the contrary, one example of the ink ribbon 14 used for the OHP sheet is shown in FIG. 13(c). The ink ribbon 14 includes the base member 15 made of resin film. The ink layer 16, the mixture of carbon and wax, is laminated on the surface of this base member 15.
In the case where this kind of ink ribbon 14 is used for printing OHP sheets, the thermal head 6 is driven to perform the cool peeling operation. That is, the ink ribbon 14 is peeled off from the OHP sheet after the melted ink layer 16 cools down and solidifies, so that the transferred ink surface becomes smooth. For this reason, it is necessary to enlarge the distance between the printing portion of the thermal head 6 and the peeling portion of the ink ribbon 14.
In this manner, there is a difference between the printing operation for the normal papers and the printing operation for the OHP sheets in the position where the ink ribbon 14 is peeled off from these recording mediums. Accordingly, the conventional thermal transfer printer, compatible with both the normal papers and the OHP sheets, usually equips a peeling roller 19 that can change the peeling position of the ink ribbon 14 as shown in FIG. 14.
Namely, a peeling lever 20 is disposed on the upper surface of the carriage 5 at the downstream of the thermal head 6 in the travelling direction of the ink ribbon 14. In the drawing, this peeling lever 20 is driven to swing between an outermost position indicated by the solid line and an innermost position indicated by the dotted line by means of an appropriate driving mechanism (not shown). This peeling lever has a peeling roller 19 provided to protrude upward at the distal end thereof. This peeling roller 19 is brought into contact with or away from the ink ribbon 14 at the downstream of the thermal head 6 in the travelling direction of the ink ribbon 14.
In the case where the peeling lever 20 is positioned at the solid-line position in the drawing, the peeling roller 19 approaches the platen 2 and is pressed against the ink ribbon 14. By delaying the peeling operation of this ink ribbon 14 from the recording medium, the ink layer in the ink ribbon 14 cools and solidifies before the ink ribbon 14 is peeled off from the recording medium. Thus, the cool peeling operation is accomplished.
On the other hand, in the case where the peeling lever 20 is positioned at the dotted-line position in the drawing, the peeling roller 19 parts from the ink ribbon 14 and positions in the ribbon cassette 21. In this case, the ink ribbon 14 is immediately peeled off from the recording medium as soon as the thermal head 6 passes. Thus, the hot peeling operation is carried out in such a manner that the ink ribbon 14 is peeled off from the recording medium during the time when the ink layer 16 of the ink ribbon 14 is in the melted condition.
However, this conventional thermal transfer printer described above uses the driving device such as a solenoid and the like to cause the swing motion of the peeling lever 20 in order to bring the peeling roller 19 into contact with the platen 2 or release it. Therefore, it is necessary to exclusively provide this driving device for operating the peeling roller 19, in addition to the driving device for bringing the thermal head 8 into contact with the platen 2 and the driving device for taking-in the ink ribbon 14.
This makes the control of the driving devices complicated. Furthermore, an overall size of the system increases as numerous devices must be installed on the carriage 5. The manufacturing cost will correspondingly increase.